1. Field of the Invention
The invention is directed to an improved actuator for superimposed steering engagement in a vehicle steering system.
2. Description of the Prior Art
With an actuator of the type with which this invention is concerned, in which the gear ratio between a change in the angle of rotation at the first input shaft and the change in the angle of rotation at the output shaft that is coaxial to the first input shaft is variable by means of an electric motor, coupled to the second input shaft, as a function of predetermined parameters, such as the rotary speed of the first input shaft, the steering angle of the vehicle wheels varies independently of the steering wheel angle, as a result of which advantages in terms of driving dynamics, safety, and riding smoothness are attained.
In a known actuator of this type, disclosed in German Patent Disclosure DE 38 30 654 A1, the superposition gear has a single-stage planetary gear with a satellite carrier, planet wheels, a sun wheel, and a ring gear; the sun wheel is connected to the first input shaft and the ring gear to the output shaft, in each case in a manner fixed against relative rotation, and the satellite carrier is connected with the second input shaft via a worm gear. The first input shaft is connected in terms of drive to the manual steering wheel, and the output shaft is connected in terms of drive to the steered vehicle wheels, and to steering gear members necessarily coupled with them. The worm gear driven by an electric motor is embodied as self-locking. Sensors are disposed on the first input shaft and on the output shaft, and their signals represent the rotary position of the shafts. The signals are delivered to a regulating device that controls the electric motor that engages the second input shaft.